A wobble plate compressor which reciprocates pistons by converting rotational movement of a cam rotor into nutational movement of a wobble plate is well known as shown in Japanese Patent Application Publication No. 58-158,382. Changing the inclined angle of the wobble plate changes the stroke length of the pistons and therefore changes the displacement volume of the cylinders.
Referring to FIGS. 1 and 2, a conventional variable displacement wobble plate compressor 1 includes front end plate 2, cylinder casing 3, valve plate 4, and cylinder head 5. Front end plate 2 is fixed on one end of cylinder casing 3 by securing bolts (not shown). Axial hole 21, which is formed through the center of front end plate 2, receives drive shaft 7. Radial bearing 8 is disposed in axial hole 21 to rotatably support drive shaft 7. An annular sleeve portion (not shown) projects from front end plate 2 and surrounds drive shaft 7, defining a seal cavity. Cylinder casing 3 has cylinder block 31 and crank chamber 32 formed therein. Cylinder block 31 has a plurality of equiangularly spaced cylinders 33 formed therein.
Cam rotor 9 is fixed on drive shaft 7 by guide pin 103. Thrust needle bearing 10 is disposed between the inner wall surface of front end plate 2 and the adjacent axial end surface of cam rotor 9. Arm portion 91 of cam rotor 9 extends in the direction of cylinder block 31. Elongated hole 92 is formed on arm portion 91. Inclined plate 11, is provided with flange portion 111, arm portion 112 and cylindrical portion 113 disposed around drive shaft 7. Arm portion 112 is formed on the outer surface of flange portion 111 and faces arm portion 91 of cam rotor 9. Hole 119 is formed in arm portion 112 and aligns with elongated hole 92. Guide pin 12, which is fixedly disposed through hole 119, is slidably movable within elongated hole 92. Ring-shaped wobble plate 13 is mounted on the outer surface of cylindrical portion 113 of inclined plate 11 through radial bearing 14. Inclined plate 11 and wobble plate 13 are disposed at an angle with respect to a plane perpendicular to the longitudinal axis of drive shaft 7. Flange portion 111 and snap ring 15 disposed on cylindrical portion 113 prevent axial movement of wobble plate 13. Wobble plate 13 is prevented from rotating by guide plate 25 which extends within crank chamber 32. Thrust needle bearing 16 is disposed in a gap between flange portion 111 and wobble plate 13. The other end of drive shaft 7 is rotatably supported through radial bearing 17 in central bore 34 of cylinder block 31. One end of piston rod 18 is rotatably connected to receiving surface 131 of wobble plate 13. The other end of piston rod 18 is rotatably connected to piston 19 which is slidably fitted within cylinder 33.
Suction ports 41 and discharge ports 42 are formed through valve plate 4 with one suction port 41 and one discharge port 42 corresponding to each cylinder 33. Suction reed valve (not shown) is disposed on valve plate 4. Discharge reed valve (not shown) is disposed on valve plate 4 opposite the suction reed valve. Cylinder head 5 is connected to cylinder casing 3 through gaskets (not shown) and valve plate 4. Partition wall 51 extends axially from the inner surface of cylinder head 5 and divides the interior of cylinder head 5 into suction chamber 52 and discharge chamber 53. Suction chamber 52 is connected to the external fluid circuit through fluid inlet port 54 formed in cylinder head 5. Discharge chamber 53 is connected to the external fluid circuit through fluid outlet port 55 formed in cylinder head 5.
Crank chamber 32 of cylinder casing 3 and suction chamber 52 of cylinder head 5 communicate with each other through conduit 311 and hollow portion 312 formed within cylinder block 31. This communication controls the angle of inclined plate 11 and wobble plate 13. Refrigerant fluid in crank chamber 32 flows to suction chamber 52 through conduit 311 and hollow portion 312 based on the operation of control valve 20. Control valve 20 opens and closes conduit 311 in response to the gas pressure in crank chamber 32. The angle of inclined plate 11 and wobble plate 13 varies in accordance with the opening and closing of conduit 311. When control valve 20 closes conduit 311 the gas pressure in crank chamber 32 gradually increases. The higher gas pressure acts on the rear surface of piston 19 to reduce the angle of inclined plate 11 and to reduce the capacity of the compressor. When control valve 20 opens conduit 311, the gas pressure in crank chamber 32 reduces thereby increasing the angle of inclined plate 11 and wobble plate 13. This increases the capacity of the compressor.
In the conventional hinge mechanism of these known compressors elongated hole 92 of arm portion 91 of cam rotor 9 is arc-shaped. The center of the arc is adjacent the connecting portion of wobble plate 13. Arm portion 112 of inclined plate 11 has hole 119, and guide pin 12 extends from hole 119.
The end of the radius of curvature of the arc of elongated hole 92 is located adjacent the connecting portion, receiving surface 131, of wobble plate 13. Thus, the axial distance between the center of guide pin 12 when the angle of inclined plate 11 is largest and when the angle is smallest is very short. The radial distance is many times longer. Also, the top clearance is the clearance between the top of piston 19 and the inner end surface of valve plate 4 at top dead center for maximum and minimum piston strokes and accounts for the re-expansion volume. The re-expansion volume is inversely proportional to the volumetric efficiency of the compressor. Accordingly, although inclined plate 11 varies from the largest angle to the smallest angle, the top clearance varies only slightly. It is necessary to greatly reduce the angle of inclined plate 11 to decrease the refrigerating capacity of the compressor.
Furthermore, when the angle of inclined plate 11 is smallest, piston 19 does not perform compression, and the reaction force against the compression force does not act on the end surface of piston 19. Therefore, it is necessary to use a return spring or similar device to return inclined plate 11 to its largest angle adjacent the side of cam rotor 9.